Many of the beds provided for X-ray computed tomography apparatuses use a structure configured to cantilever a top on which an object is placed. This structure allows a reduction in installation space and has superiority in enlarging a work area for an operator. However, the top is inevitably subjected to so-called “warp”, that is, deforms downward due to its own weight and the weight of an object.
Conventional methods have used physical and mechanical measures for suppressing the warp of the top, e.g., using a mechanism for supporting the top and improving the rigidity of the top itself. These measures can reduce the warp of the top due to the gravity of the earth but cannot avoid the warp because of the structure configured to cantilever the top.
Owing to this problem, when volume scanning is repeated while the scan position is changed along, for example, the rotation axis of the X-ray tube (Z-axis; approximate to the body axis of an object), an overall image obtained by synthesizing scanned images along the Z-axis has apparent differences in level at the volume scan switching positions. As a consequence, the overall image becomes discontinuous.
In order to solve this problem, a method of measuring the relationship between the position of a top and a warp amount in advance and shifting an image position in accordance with the measurement is often used. These solutions involve a problem of requiring preliminary scanning. The method of solving the problem by shifting images involves a problem of incapability of substantially solving the problem of differences in level (discontinuity) because the warp amount of the top is smaller than the pixel pitch or is not an integer multiple of the pixel pitch.